The use of transgenic animals is a powerful and informative approach that has been successfully undertaken by the core PL for over five years to study neurodegenerative diseases. The purpose of the transgenic core is to extend production of mouse models of Down's syndrome (Ts21), Alzheimer's disease (AD), and other neurodegenerative disorders and to generate novel crosses between existing models, including mice showing endocytic-autophagic-lysosomal system (EALS) pathology. The Ts65Dn mouse model develops endosomal abnormalities similar to those in AD and is used by all the projects. In order to modulate the endocytic pathology in these mice, they will be crossed with mice expressing human APP, null for mouse APP, or APP-secretase deficient. In human AD, inheritance of the ApoE D4 allele exacerbated endosomal alteration, which will be further examined in Ts65Dn crossed to humanized ApoE mice. The role for APP triplication in AD-related endosome dysfunction in these mice will be explored by single-cell DMA microarray analyses using Ts65Dn and Ts65Dn/APP null crosses. The second Project has identified a key role for presenilin in modulating autophagy, which will be examined in PS1 hypomorphic and a mutant PS1 transgenics and further explored in crosses with Ts65Dn and an amyloid depositing mouse. A transgenic overexpressing LC3, a regulator of autophagy, will be used as a model of autophagy dysregulation. The third Project will define the neuroprotective role that cystatin C plays in of AD-related EALS dysfunction using these same mouse models. Modulation of cystatin C levels will be obtained by crossing these models with either cystatin C transgenic or knockout mice. The potential for redundancy between cystatin B, another cysteine protease inhibitor, and cystatin C will be investigated by using cystatin B knockout mice. The core leader has extensive experience managing a large mouse colony with complex breeding schemes, and will be able to co-ordinate animal breeding, genotyping, and tracking of animals.